1. Field of the Invention
The invention concerns an X-ray tube anode, more particularly a rotating anode of the type having a main body that bears a target formed by a surface layer of an X-ray emitting material.
2. Description of the Prior Art
In X-ray tubes, notably those used for X-ray diagnosis, the X-radiation is obtained under the effect of an electron bombardment of a layer of a target material, i.e. generally a material, with a high atomic number, that is refractory and is a good conductor of heat such as, for example, tungsten, molybdenum or an alloy containing at least one of these elements. These are the most commonly used elements, but the invention is not restricted to an anode with an emissive material containing these elements or their alloys.
The target layer is bombarded on a small surface, called a focal spot, forming the source of the radiation.
For a long time now, the high instantaneous power values (of the order of 100 KW) used and the small dimensions of the focal spot have led to the use of rotating anodes in order to distribute the heat flux over a greater area than that of the focal spot so as to dissipate it more efficiently.
This distribution and dissipation of heat is all the more efficient as the linear speed of rotation of the anode is high.
However, this linear speed is limited by the mechanical strength of the anode and, notably, the risks of its breaking up due to the formation of cracks, notably in the material forming the target layer, which spread into the other materials forming the anode.
In fact, rotating anodes are generally formed by a base or substrate forming a block with a regular shape such as the shape of a disk, a cone or similar shape, on which one or more layers of an X-ray emitting material or target material are deposited. Generally, the adhesion of the layer of target material to the base is improved by the deposition of an intermediate anchoring layer thus creating a certain continuity between the emitting material and the material forming the substrate, for example by surface diffusion of the anchoring material into the other two materials or vice versa. This continuity may favor the spread of the cracks generated in the emitting material.
The invention is designed notably to overcome these drawbacks by proposing an anode comprising a particular structure that prevents the cracks, caused in the emitting material, from spreading towards the base or substrate, or from spreading in the reverse direction.